In prior known collision avoidance systems as for example, the system disclosed in U.S. Pat. No. 3,737,902, a highly sophisticated (and costly) collision avoidance system is married to a radar system and a large computer. This complex system is applicable only to large ships with highly sophisticated electronics equipment and requires highly skilled personnel for its operation. The present invention provides for a closest point of approach calculator that is a small, inexpensive, manually operated collision avoidance device that can be operated by unskilled personnel, and may be used aboard any ship, military or commercial, having a radar or other system of determining the location of target vessels.